This invention relates to in vivo monitoring one or more solutes in a biological system using optical techniques.
Monitoring the concentration of a solute (e.g., low molecular weight carbohydrate or polyhydroxy compounds such as sugars (mannitol, sorbitol, fructose, sucrose, or glucose), alcohols (methanol, ethanol, or propanediol), and electrolytes (sodium, potassium, magnesium, calcium, or chloride ions)) in a biological system has important applications in the medical field. For example, it is important for diabetics, who have gone off insulin, to monitor their glucose level so that can remedy any serious deviation in the level before harm occurs.
Near infra-red radiation (NIR) has been used to study non-invasively the oxygen metabolism in tissue (for example, the brain, finger, or ear lobe). Using visible, NIR and infra-red (IR) radiation for medical imaging could bring several advantages. In the NIR or IR range the contrast factor between a tumor and a tissue is much larger than in the X-ray range. In addition, the visible to IR radiation is preferred over the X-ray radiation since it is non-ionizing; thus, it potentially causes fewer side effects. However, with lower energy radiation, such as visible or infra-red radiation, the radiation is strongly scattered and absorbed in biological tissue, and the migration path cannot be approximated by a straight line, making inapplicable certain aspects of cross-sectional imaging techniques.